Fix highlighting when editing in patch review

Summary:
Problems:
- removing markers in foreach loop lead to crash (BUG 380125)
- highlighting when editing in patch review was broken
- reloading would stop the highlighting

Fixes:
- textInserted/textRemoved signals only send line-by-line
  (or character-by-character) changes and there are
  extra signals for newline insertion/removal. The patch
  reflects this mechanism.
- Redo the highlighting when the document is reloaded.
- Remove one of the duplicated lists of ranges (mainly
  to improve maintainability).

Persisting Issue:
- possible dangling mark when removing the "wrong"
  newline from a set of newline-only-lines changes.

BUG: 380125

Test Plan:
- tested text insertion, text removal and mark clicking and the
  combination of those with (mostly) consistent results for a git diff

Reviewers: #kdevelop, apol

Reviewed By: #kdevelop, apol

Subscribers: kdevelop-devel

Differential Revision: https://phabricator.kde.org/D6398